CONDITION

Portosystemic Shunt

Why this matters now

Congenital portosystemic shunts are present from birth and often become apparent in young animals, typically within the first year of life. Certain breeds are predisposed, including Yorkshire Terriers, Maltese, Pugs, and Irish Wolfhounds in dogs, and Himalayan and Persian cats. Acquired shunts can develop at any age, usually secondary to liver disease. Signs may be subtle initially and often fluctuate, sometimes leading to delayed recognition.

Clinical signs typically develop gradually and may wax and wane, often relating to meals. The accumulation of toxins, particularly ammonia, affects brain function, causing a range of neurological signs from subtle behavioural changes to more obvious symptoms. Affected animals often fail to thrive, remaining smaller than littermates. Without management, episodes may become more frequent and severe. The liver typically remains underdeveloped due to receiving inadequate blood flow.

Signals & patterns

Early signals

Smaller size compared to littermates

Reduced liver function and nutrient processing often results in poor growth and smaller body size.

Intermittent lethargy or dullness

Episodes of unusual tiredness, particularly after meals, as toxin levels fluctuate.

Excessive drinking and urination

Altered kidney function and reduced ability to concentrate urine leads to increased water intake and output.

Prolonged recovery from sedation or anaesthesia

The liver's reduced ability to metabolise drugs results in prolonged drug effects.

Later signals

Obvious neurological signs

Disorientation, aimless wandering, circling, head pressing, or apparent blindness, particularly after eating.

Seizures

Severe toxin accumulation can trigger seizure activity.

Drooling

Excessive salivation, particularly in cats, may occur during neurological episodes.

Urinary problems

Formation of specific types of bladder stones (urate) is common, potentially causing straining or blood in urine.

Click to read about the biological mechanisms

How this is usually investigated

Diagnosis involves blood tests to detect signs of reduced liver function, followed by imaging to identify the abnormal vessel. Thorough evaluation helps plan management.

Blood tests including bile acids

Purpose: To assess liver function indirectly by measuring substances the liver normally processes
Considerations: Fasting and post-feeding bile acid levels are typically measured. Elevated levels suggest blood is bypassing the liver but do not confirm the cause.

Blood ammonia levels

Purpose: To measure this key toxin directly
Considerations: Requires careful sample handling. Elevated ammonia during clinical signs supports hepatic encephalopathy.

Abdominal ultrasound

Purpose: To visualise the liver and potentially identify the shunt vessel
Considerations: The liver is typically small. Shunt vessels may be visible with experienced ultrasonographers. Some shunts are difficult to identify.

CT angiography

Purpose: To provide detailed imaging of blood vessels and precisely identify shunt location
Considerations: Often preferred for surgical planning. Requires general anaesthesia. Provides detailed anatomical information.

Urinalysis

Purpose: To check for ammonium urate crystals
Considerations: Presence of these crystals supports the diagnosis. May identify concurrent bladder stones.

Options & trade-offs

Management can be medical, surgical, or a combination. The approach depends on shunt type, severity, and individual circumstances. Many animals can lead good quality lives with appropriate management.

Dietary management

Feeding a moderately protein-restricted, highly digestible diet to reduce ammonia production.

Trade-offs: Forms the foundation of medical management. Requires dietary compliance. May need adjustment based on response.

Medications to reduce toxin absorption

Lactulose and antibiotics to trap ammonia in the gut and reduce ammonia-producing bacteria.

Trade-offs: Can significantly reduce clinical signs. Requires ongoing medication. Dose often needs adjustment.

Surgical correction

Procedures to gradually close the shunt vessel, redirecting blood flow through the liver.

Trade-offs: Can be curative for congenital single shunts. Requires specialised expertise. The liver must develop capacity to handle blood flow, which may take time.

Interventional radiology

Minimally invasive placement of devices to close the shunt from within the blood vessel.

Trade-offs: Alternative to open surgery. Requires specialised facilities and expertise. May be appropriate for certain shunt types.

Long-term medical management

Continued dietary and medical therapy without surgical intervention.

Trade-offs: May be chosen when surgery is not feasible or preferred. Many animals maintain reasonable quality of life. Requires commitment to ongoing management.

Common misconceptions

Misconception:

"Neurological signs are always severe and constant"

Reality:

Signs often fluctuate, ranging from subtle behavioural changes to more obvious episodes. They may worsen after eating and improve between meals.

Misconception:

"Surgery is always necessary"

Reality:

Whilst surgical correction can be curative, many animals are managed successfully with diet and medication alone, particularly if they respond well to medical management.

Misconception:

"Affected animals cannot live good quality lives"

Reality:

With appropriate management, whether medical or surgical, many animals with portosystemic shunts can live comfortable lives, though monitoring remains important.

Noting whether signs seem to follow any pattern, such as worsening after meals or improving with fasting, can provide important diagnostic clues. Documenting the specific behaviours observed during episodes helps distinguish neurological signs from other causes. Keeping track of water intake and urination patterns may also be useful for veterinary discussions.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS